chez:

 

All good now. The plumber came back and sorted it out. Apparently, there was some debris from the old waste pipe. He used a plunger to shake it up and then run the tap to push water to anything that caused the air block. He did it for less than 5 mins. I'm guessing that he did not check the flow after the installation last time, otherwise, he could have picked it up. No charge. Overall, I'm pleased. 

 

Yep - pretty much as I said.

https://www.geekzone.co.nz/forums.asp?forumid=141&topicid=293080&page_no=1#2838941